If a shared file is concurrently edited by a plurality of users and saved, there is a possibility that the shared file loses its consistency and is then damaged.
Conventionally, in the case of editing the shared file, exclusion control is carried out with respect to each shared file. That is, when the shared file is being used by a user, the other users cannot open or edit the shared file.
According to the exclusion control with respect to each shared file, when a user tries to open a shared file, whether or not the shared file is locked is checked first. In the case in which the shared file is not locked, the shared file is locked for the user and becomes openable and/or editable. In the case in which the shared file has already been locked by the other user, the user cannot open or edit the shared file.
It is easy to realize such exclusion control. However, in this case, it is impossible to concurrently edit one shared file. Therefore, the larger the shared file is, the worse the efficiency of the editing work becomes.
In order to solve this problem, Document 1 (Japanese Laid-Open Patent Publication No. 1994/12310 (Tokukaihei 6-12310, published on Jan. 21, 1994) discloses a technique for allowing concurrent editing of a shared file by carrying out the exclusion control that controls access to sectional regions of the shared file on a regional basis (i.e. controls the access to the sectional regions individually).
As illustrated in FIG. 8, when starting editing a sectional region 102a of a shared file 101, an information processing terminal 104a inquires an exclusion information processing section 105a about whether or not the editing can be carried out with respect to the sectional region 102a. The exclusion information processing section 105a looks up an exclusion control information 103 so as to check if the editing can be started or not. Initially, the editing is not carried out with respect to the sectional region 102a. Therefore, in the exclusion control information 103, the exclusion control information concerning the sectional region 102a is empty initially. This indicates that the editing can be started. The exclusion information processing section 105a informs the information processing terminal 104a that it is possible to start the editing. The information processing terminal 104a thus informed can start the editing with respect to the sectional region 102a. When the information processing terminal 104a has started editing the sectional region 102a, the exclusion information processing section 105a writes to the exclusion control information concerning the sectional region 102a in the exclusion control information 103 that the sectional region 102a is being edited.
In the case in which an information processing terminal 104b intends to start editing the sectional region 102a while the information processing terminal 104a is editing the sectional region 102a, an exclusion information processing section 105b looks up, in the same way as above, the exclusion control information concerning the sectional region 102a in the exclusion control information 103 to check if the editing can be carried out with respect to the sectional region 102a. In this case, unlike the above case, the exclusion information processing section 105b finds out that the sectional region 102a is being edited by the information processing terminal 104a. Therefore, the exclusion information processing section 105b informs the information processing terminal 104b that the editing of the sectional region 102a is prohibited. On this account, the information processing terminal 104b thus informed cannot start editing the sectional region 102a. 
In the case in which the information processing terminal 104b starts editing a sectional region 102b of the shared file 101, the above-described process is carried out in a similar way. In this case, the information processing terminal 104b can start editing the sectional region 102b. 
Thus, by carrying out the exclusion control with respect to the sectional regions (102a, 102b, . . . ) of the shared file 101 on the regional basis, it becomes possible to concurrently edit the shared file without losing its consistency. Here, in the case in which the shared file 101 has a relevant sectional region logically relevant to or integrated with the sectional region (102a, 102b, . . . ) to which the editing is carried, the technique is so arranged that the exclusion control can be carried out with respect to the relevant sectional region in the same way as above.
However, in the above arrangement, in the case in which the shared file 101 is edited by a plurality of users, all the contents in the shared file 101 are displayed for all the users with a common display layout peculiar to the shared file 101. However, such common display layout may not be easy to use or look at for the respective users. Therefore, each user starts editing after consuming some time to find out, from all the contents of the shared file 101 of such common display layout, a sectional region (for example, the sectional region 102a) where the user wishes to edit. Moreover, in the case in which the user refers to the relevant sectional region during the editing, it is necessary to look for the relevant sectional region in the same way as above. On this account, the editing becomes inefficient. Furthermore, the larger the shared file 101 is, the more serious these problems become.